Issue |
A&A
Volume 627, July 2019
|
|
---|---|---|
Article Number | A65 | |
Number of page(s) | 20 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/201935469 | |
Published online | 01 July 2019 |
Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium★
1
Departamento Ciencias Integradas, Facultad de Ciencias Experimentales, Centro de Estudios Avanzados en Física, Matemáticas y Computación, Unidad Asociada GIFMAN, CSIC-UHU, Universidad de Huelva,
Spain
e-mail: miguel.carvajal@dfa.uhu.es
2
Instituto Universitario “Carlos I” de Física Teórica y Computacional, Universidad de Granada,
Granada,
Spain
3
INAF – Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
Firenze
50125, Italy
4
Université Grenoble Alpes, CNRS, IPAG,
38000
Grenoble,
France
5
Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS 7583, Université Paris-Est Créteil, Université de Paris, Institut Pierre Simon Laplace (IPSL),
Créteil, France
6
Department of Astronomy, University of Michigan,
311 West Hall, 1085 South University Avenue,
Ann Arbor,
MI 48109, USA
Received:
14
March
2019
Accepted:
28
May
2019
We emphasize that the completeness of the partition function, that is, the use of a converged partition function at the typical temperature range of the survey, is very important to decrease the uncertainty on this quantity and thus to derive reliable interstellar molecular densities. In that context, we show how the use of different approximations for the rovibrational partition function together with some interpolation and/or extrapolation procedures may affect the estimate of the interstellar molecular column density. For that purpose, we apply the partition function calculations to astronomical observations performed with the IRAM-30 m telescope towards the NGC 7538–IRS1 source of two N-bearing molecules: isocyanic acid (HNCO, a quasilinear molecule) and methyl cyanide (CH3CN, a symmetric top molecule). The case of methyl formate (HCOOCH3), which is an asymmetric top O-bearing molecule containing an internal rotor is also discussed. Our analysis shows that the use of different partition function approximations leads to relative differences in the resulting column densities in the range 9–43%. Thus, we expect this work to be relevant for surveys of sources with temperatures higher than 300 K and to observations in the infrared.
Key words: techniques: spectroscopic / ISM: abundances / radio lines: ISM
Tables D.1–D.3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A65
© M. Carvajal et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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